1. Field of the Invention
The present invention relates to a roller bearing cage applied to, for example a lower, larger end called a rod “big end” of a connecting rod in an engine and more particularly to a roller bearing cage suitable for use in a split shell roller bearing designed to fit around a crankshaft in which crankpins are made integrally with crank webs.
2. Description of the Prior Art
As the modern engines are needed to get further higher in horsepower, the crankshaft for the powerful engines has to be made so as to stand up to further high-speed revolution. To cope with this, the crankpins are made integral with the crank webs to enhance the rigidity or stiffness of the crankshaft. Split shell roller bearings, because of the integral construction of the crankpin with the associated crank webs, are inevitably required at the rod big-ends of the connecting rods and correspondingly the cage is also needed to be made in any split type. High-compression, high-speed engines, moreover, impose very harsh conditions to the bearings.
An example of conventional bearing cages is disclosed in Published Unexamined Patent Application in Japan No.H08-219 149. The prior bearing cage is made in a configuration resembling any gate in cross section and envisaged to carry effectively the loads imposed by modern high-speed engines. To this end, the cage is made on the outside periphery thereof with the retaining projections to keep the rollers against their escape out of the cage.
Another example of the bearing cage having a gate-like configuration in cross section is disclosed in Published Unexamined Utility Model Application in Japan No.H01-168 014. The prior bearing cage is also directed to keep the rollers against their escape out of the cage, thereby carrying well the heavy loads imposed by high-speed engines. To this end, the bearing cage, as illustrated in FIG. 1 of the above citation, has a partition separating two adjacent pockets, the thin area of which is made with projections that extend inside the pockets slightly beyond the flanks of the thickened areas to serve for keeping the rollers against their radially outward escape out of the cage.
Published Unexamined Patent Application in Japan No. 2 000-240 660 discloses a roller bearing retainer split into two haves, which is favorable for the crankshaft having crankpins formed integrally with the crank webs. The prior roller bearing retainer is designed in such a way reduced in an outside diameter thereof as nearing the diametral opposing abutment ends of the retainer halves to be made in a somewhat oval shape. The construction recited above is envisaged to keep the retainer against any unfavorable deformation where the retainer may get bulged radially at the diametral opposing abutment ends of the retainer halves.
Another split type of the roller bearing cage is disclosed in Published Unexamined Utility Model Application in Japan No.H06-6 746, in which an annular cage of true round is split into two halves along a diametral plane lying on the circumferential midway points of any two diametral opposing cage bars. The cage halves are covered with any coating material of a preselected thickness at their at least any one side of split ends that come into circumferential abutment against one another.
Moreover, Published Unexamined Patent Application in Japan No.H09-72 332 discloses a connecting-rod bearing construction for marine engines, in which a needle bearing for a rod big-end is composed of a pair of semicircular cage halves, which come into abutment against each other to form a completely circular cage.
None of the prior bearing cages of split type recited earlier, nevertheless, succeeds in overcoming a major problem in which the split cage is much subject to deformation of bulging radially outwardly at the abutment ends of the cage halves owing to large centrifugal force taking place when the bearing revolves at high speed. This will cause the bearing to seat improperly in the bore surface in the rod big-end of the connecting rod, thus resulting in bearing failure such as lack of lubricating oil, seizing or binding between the bearing and the connecting rod, and so on.
An example of the prior bearing cages of split type envisaged to resolve the problem stated just above is illustrated in FIG. 11. The prior split-type bearing cage 40 is generally composed of a pair of semicircular cage halves 41, which are chamfered at a corner 39 where the abutment ends of the semicircular cage halves 41 merge with the outside peripheral surface of the cage. Rollers 43 are installed in pockets arranged circumferentially of the cage.
With the prior bearing cages of split type constructed as stated earlier, chamfering work on the corners is done to the semicircular cage halves 41, separately, which have been previously prepared by splitting a cylindrical cage stock. This chamfering procedure is much unfavorable for precision control of the chamfered area 39 in size. Thus, not only the chamfered area 39 get scattered in their sizes, but also an edge where the chamfered area merges with the associated outside periphery 42 of the cage will tend to be made much sharp. The tendency will cause any likelihood of raising the lack of lubricating oil, the seizing of bearing and so on at the abutment ends 38 and any area nearby the ends. With the prior bearing cages of split type, moreover, as the cylindrical cage is usually subject to heat treatment in preparatory to cutting into semicircular cage halves 41, the resulting cage halves can't help spreading somewhat radially outwardly at the time of cutting. This also makes it tough to prepare the chambered area at the corner with high precision.